Electric power steering device, control device for electric power steering device, and program

Abstract

An electric power steering device 100 includes: an electric motor 110 configured to apply a driving force to steer a wheel in response to operation of a steering wheel; and a control device 10 configured to perform control of drive of the electric motor by estimating a degree of sloping in a transverse direction of a roadway on which a vehicle travels, determining, based on the estimated degree of sloping, a correction current for correcting a target current required for the electric motor to generate the driving force, and correcting the target current with the correction current.

The invention claimed is: 
     
       1. An electric power steering device comprising:
 an electric motor configured to apply a driving force to steer a wheel in response to operation of a steering wheel; and 
 a control unit configured to perform control of drive of the electric motor by estimating a degree of sloping in a transverse direction of a roadway on which a vehicle travels, determining, based on the estimated degree of sloping, a correction current for correcting a target current required for the electric motor to generate the driving force, and correcting the target current with the correction current, wherein 
 the control unit is configured to: 
 determine conditions of a road surface of the roadway and change the control according to the determined conditions of the road surface; and 
 perform the control when the road surface is paved, and not to perform the control in response to determining that the road surface is unpaved when a number of times where a differential value for an indicator representing the degree of sloping is greater than a predetermined first threshold exceeds a second threshold during a unit of time. 
 
     
     
       2. The electric power steering device according to  claim 1 , wherein the control unit is configured to determine a slope current using a slope current map defining correspondence between the estimated degree of sloping and a slope current, and determine the correction current by multiplying the slope current by a vehicle speed gain determined by a vehicle speed. 
     
     
       3. The electric power steering device according to  claim 2 , wherein the control unit is configured to perform the control by correcting a difference in a lateral height of the vehicle caused by a slope in the transverse direction of the roadway and/or traveling of the vehicle. 
     
     
       4. The electric power steering device according to  claim 1 , wherein the control unit is configured to estimate the degree of sloping based on lateral acceleration detected by a lateral acceleration sensor and centripetal acceleration calculated from a yaw rate acting on the vehicle and a vehicle speed. 
     
     
       5. The electric power steering device according to  claim 4 , wherein the control unit is configured to perform the control by correcting a difference in a lateral height of the vehicle caused by a slope in the transverse direction of the roadway and/or traveling of the vehicle. 
     
     
       6. The electric power steering device according to  claim 1 , wherein the control unit is configured to perform the control by correcting a difference in a lateral height of the vehicle caused by a slope in the transverse direction of the roadway and/or traveling of the vehicle. 
     
     
       7. The electric power steering device according to  claim 1 , wherein
 the electric motor is configured to apply the driving force via a rack shaft, and 
 the control unit is configured to perform the control by taking into account an axial load that is experienced by the rack shaft due to a slope in the transverse direction of the roadway. 
 
     
     
       8. The electric power steering device according to  claim 7 , wherein the control unit is configured to calculate the axial load by using a knuckle arm length and a distance between a center of a kingpin and a point where the wheel contacts a road surface. 
     
     
       9. A control device for an electric power steering device, the control device comprising:
 a slope estimator configured to estimate a degree of sloping in a transverse direction of a roadway on which a vehicle travels; 
 a road surface determiner configured to determine conditions of a road surface of the roadway; 
 a correction current determiner configured to determine, based on the conditions of the road surface of the roadway determined by the road surface determiner and the estimated degree of sloping, a correction current for correcting a target current required for an electric motor to generate a driving force; and 
 a target current determiner configured to determine the target current based on the determined correction current, wherein 
 the road surface determiner is configured to determine that the road surface is unpaved when a number of times where a differential value for an indicator representing the degree of sloping is greater than a predetermined first threshold exceeds a second threshold during a unit of time, and determine that the road surface is paved when the number of times does not exceed the second threshold during the unit of time, and 
 the correction current determiner is configured to determine the correction current based on the estimated degree of sloping when the road surface is paved, and set the correction current to 0 when the road surface is unpaved.